1. Field of the Invention
The present invention relates to the field of liquid crystal display, and in particular to a method for multiplying current of an LED light bar and associated driving circuit thereof.
2. The Related Arts
LED is a solid state light source, which uses re-combination of electrons and electron holes in a semiconductor to emit photons. The color emitting from an LED is determined by the energy of photons and the energy of photons is determined by the material used. The same material gives substantially identical wavelength of the emitted light and thus, each LED gives off a pure color. The most commonly known LEDs of regular brightness include red color and green color. The LEDs have small sizes of die, have diversified colors, and provide significant flexibility in arrangement for use, these being the factors making them superior to the ordinary light source. Further, compared to the other light sources, the LEDs also provide relatively high light efficiency and relatively high reliability and the way of power supplying thereto is relatively simple. Thus, the LEDs are particularly fit to serving as a light source for displaying.
Similar to a PN junction of a regular semiconductor, voltage drop of forward conduction of an LED hardly varies with conduction current and is generally approximately 3.5V, but the illumination increases with the increase of the current flowing therethrough, so that the larger the current is, the larger the optic output and illumination will be. Thus, LEDs must use serially-connected power supply and a constant current power supply, so that the electrical current flowing through the diode is constant in order to maintain stable optical output. For a driving chip for LEDs, the output must feature constant current to power serially connected LEDs. Thus, using an LED constant current driving chip to drive an LED light bar is thus put into use.
Referring to FIG. 1, in the state of the art, when electricity is applied to an LED constant current driving chip, a constant voltage is generated therein. This voltage and a resistance R100 that is externally connected to a current setting pin of the constant current driving chip 200 collectively determine the current flowing through an LED light bar 100. Being constrained by the semiconductor manufacturing process and the issue of heat emission, the maximum current that an individual channel of the LED constant current driving chips 200 available from every manufacturer can take is 300 mA. With the progress of science and technology, currently, the size of liquid crystal display panel is getting larger and larger and higher and higher backlight luminance is desired for the liquid crystal display panel. The conventional LED backlight driving circuits often uses an individual constant current driving module contained in an LED constant current driving chip to drive a single LED light bar, this making it impossible for the current flowing through the LED light bar to reach a level exceeding 300 mA. Due to such a limitation of the driving current, the LED light bar cannot provide a brighter light source and does not meet the need of large-sized liquid crystal displays.